New evidence for strong intergalactic magnetic fields may help
to solve the mystery of ultrahigh-energy cosmic rays. These
particles can reach energies of more than 1020 eV –
100 million times as high as particle beams produced in
accelerators on Earth.
At the May meeting of the
American Physical Society, Phil Kronberg of the University of
Toronto presented low-frequency (75 MHz) radio images of
parts of the Great Wall supracluster of galaxies. The observations
showed a diffuse synchrotron glow in the regions outside the
galaxy clusters, revealing the presence of magnetic
fields.
New combined X-ray and radio observations of the
clusters has improved the accuracy of measurements of both the
magnetic field strength and the density of space in these regions.
The team measured the Faraday rotation (the rotation of the
plane of polarization) of the radio waves.
The results show
intergalactic magnetic fields that are many times stronger than
those within the much denser disc of the Milky Way. This means
that a significant amount of energy is stored within the
intergalactic gas.
This raises important questions about the
origin of magnetic fields – whether they were seeded by the first
generations of stars and galaxies or result from earlier activity
when the universe was less than 1 s old.
